Field of the Invention
The invention relates to the field of cartridged ammunitions and, more particularly, to the field of mounting or blocking projectiles in cartridge cases.
Description of the Related Art
The metal case cartridge with a bottle shape and a center fire is universally used for all light weaponry. It has remained essentially unchanged since its invention at the end of the XIXth century.
It consists, as shown in FIG. 1, in a tubular case 1 made of brass, or even steel, containing a propellant powder charge 2 and receiving, at a first longitudinal end 3, a head 4 with a primer 5, and having, at its other longitudinal end 6, a diameter reduction forming an external shoulder 7 and then a neck 8 and a projectile 9, with an ogival-shaped nose 91 and a base 92 having a first portion of a constant diameter, followed by a second portion whose diameter decreases up to its head 93, said projectile being forcibly pressed into or even crimped in the neck 8 at this first portion of the base. The shoulder is intended to cooperate with a part of the weapon of a complementary shape allowing to reproducibly position the cartridge longitudinally.
This case fulfills several roles:                It ensures the mechanical integrity of the shot during the handling and loading phases, which can be brutal in the case of automatic reloading weapons,        It ensures, by its neck, a repeatable positioning of the projectile, partially guaranteeing the accuracy of the system, as well as a regular pull-out force of the projectile for ensuring optimal and repeatable internal ballistics,        On the one hand, when firing the shot and under the action of the pressure forces, the case body elastically deforms and ensures the (rear) sealing of the chamber and prevents any burnt gas blowback towards the gunner and, on the other hand, when the pressure drops, the case returns to its original dimensions allowing its extraction at the end of the cycle,        By its design, the head should not deteriorate in order to avoid any gas leakage around the primer, or worse, an ejection thereof.        
It can be noted that the neck has itself a central role, since it ensures:                the interface between the case and the projectile,        a good concentricity of the shot,        a pull-out force as constant as possible over the whole temperature range,and it is constrained both on its external diameter, determined by the weapon chamber, and on its internal diameter, determined by the diameter of the projectile.        
In addition, due to the geometry of a bottle-shaped case, such as that of FIG. 1, which is implemented in most modern military ammunitions for long weapons, the connection between the conical shoulder 7 and the cylindrical neck 8 is a stress concentration area likely to produce a separation of the two, the neck 8 remaining “stuck” in the chamber while the remainder of the case is extracted, preventing the weapon from being reloaded.
Furthermore, a case accounts for about 50% of the mass of the shot, and 50% of its price, this part increasing constantly due to the rising price of copper, which is the major component of brass.
Significant efforts have been undertaken to try to reduce, or even eliminate, this element and thus reduce by 50% the mass of ammunitions.
A first solution consisted in working on ammunitions whose propellant charge itself ensured the mechanical integrity of the shot, with the sealing of the chamber being ensured by the mechanical design thereof. These efforts culminated in the “near acceptance” of the G11K2 rifle by the German army during the 80s, and of its caseless 4.7×33 mm ammunition.
However, this type of cartridge has a number of disadvantages, such as:                the aging of the sealing ring of the chamber,        an auto-ignition risk in case combustion residues are present,        a risk of contamination of the weapon by bits of powder in case of a mis-insertion of the ammunition in the chamber.        
A second solution was the replacement of the brass or steel case by a case made of a light alloy or composite materials, allowing to reduce by ⅔ the mass of the case, namely an overall mass saving of the cartridge of about 33%.
The use of metals lighter than brass or steel has been suggested. However, there is no aluminum alloy having both the required toughness for holding the primer and a yield strength avoiding the formation of cracks on the body of the case. Indeed, either the head resists and cracks appear on the body, or the body resists but leaks appear at the head. Moreover, in case the case breaks, aluminothermy phenomena happen, with the case partially consuming itself generating hot spots that can cause the destruction of the weapon. Therefore, the applications of light alloy cases are limited to some handgun ammunitions involving a low chamber pressure.
In parallel, the use of technical polymers, especially the technical polymers referred to as “high temperature” technical polymers, has also been suggested. In this respect the patent application U.S. Pat. No. 2,862,446 is known, which describes, as shown in FIG. 2, a cartridge comprising a polymer tubular case 11 containing a propellant powder charge 12 and receiving, at a first longitudinal end 13, a metal head 14 with a primer 15, and having, at the other longitudinal end 16, a diameter reduction forming a shoulder 17 and then a neck 18 molded on a projectile 19.
However, the use of such cartridges is facing many difficulties, namely:                When making cases by injection, the neck, whose thickness is generally lower than that of the rest of the case, can have irregularities caused by a mis-filling of the mold, which is a source of waste.        The lower mechanical strength of the polymer compared to that of brass implies using thicker walls, which reduces the loading volume of the case by the order of about 15%,        This reduction of the loading volume of the case implies using, with an identical projectile and for identical performance, a compressed charge and, consequently, increasing the maximum chamber pressure,        When inserting the projectile, the neck inflates, shortens and can crack.        When firing, it can happen from time to time, between once in a hundred times and once in a thousand times, that the neck separates from the case and remains welded to the chamber. While this incident rate is acceptable for a “civilian” application, it is incompatible with a military application.        
Also known is patent WO03036221 which describes a cartridge comprising, on the one hand, a projectile with an ogival-shaped nose and a base ending with a head and, on the other hand, a polymer neckless tubular case delimiting a propellant powder receiving chamber closed at a first longitudinal end by a head with a primer and closed at the second end, opposite to the first end, by the base of the projectile, with a portion of the neckless tubular case enclosing a portion of the projectile and having itself, at least in part, a frustoconical external shape.
However, such a projectile comprises a combustion chamber of the same diameter as that of the projectile which considerably limits the range of the projectile and does not allow, for example, to replace the “bottleneck” or “bottle”-type metal cartridges with a 5.56- or 7.62-caliber metal case, such as that shown for example in FIG. 1, by this type of cartridge, but only to use them for exercises on targets at a short distance.